Investigation Of The Coupling Technique Based On Using Chlorella Vulgaris To Degrade The High Organic Loaded Wastewater

Energy security and environmental probelem are the common concern in the worldwide. Microalgae culture provide a biotreatment to remove the carbon, nitrogen and phorphous in the wastewater coupled with the production of potentially valuable biomass, which can be used for production of bio-diesel. It is an optimal way to achieve an improvement of environment and effective the utilization of the waste resource. But some of wastewater have high concentrations or containing toxic organic compounds or heavy metals which inhibits the algal growth. Therefore, a proper pre-treatment is needed to improve the wastewater quality for providing the demand of culturing algae. The feasibility and effectiveness of the electrochemical pretreatment and adsorbents addition for improving the high concentrations wastewater treatment by algal biological methods were investigated in this work.The electrochemical oxidation as a pretreatment coupled with algal biological process for wastewater treatment may improve the pollutants removal efficiency as well as the algal biomass production. In this study, the anaerobic digested effluents were pretreated by electrolysis, and then the pretreated wastewater was used as nutrients medium to cultivate the microalgae for pollutans removal and algal biomass production. The results indicated that the electrochemical pretreatment can efficiently remove the ammonium nitrogen (NH4+, total phosphorus (TP), total organic carbon (TOC), total carbon (TC), turbidity and bacteria in the digested effluents. About 100.0% of NH4+, turbidity and bacteria, 97.6% of TP,81.5% of TOC and 96.6% of inorganic carbon (IC) were removed by 5 h electrochemical treatment under experimental condition, respectively. The anaerobic digested effluents pretreated by electrolysis after 2 h obviously promoted the biodegradability of the wastewater for algae cultivation. The pollutants removal amounts by the combination of electrolysis and biological treatment were much higher than the other combinations. Results indicated the feasibility of the combination of the electrolysis and biological treatment for wastewater treatment. The electrolyte existed in the watstwater significantly improved the indirect oxidization of electrolysis and the ammonium removal efficiency. The ammonium removal kinetics correlated to the electrolyte concentrations, i.e. with insufficient amount of NaCl electrolyte in the wastewater, the ammonium removal followed the pseudo first-order reaction. While, with sufficient amount of NaCl, the ammonium oxidation rate was independent of ammonium concentrations and followed the pseudo zero-order kinetics. In addition, the organics in the wastewater had inhibition effect on ammonium removal. Adding adsorbents also significantly improved the wastewater treatment. This study also investigated the wastewater treatment and algal-bacteroal biomass growth in the menbrane photo-bioreactor (MPBR) when adding zeolite as an adsorbent. It is found that the stability of the algal-bacterial system, as well as the pollutants removal and the biomass production were improved by adding zeolite. Zeolite had a high efficiency for ammonium removal. Batch test results showed that 71% ammonia can be removed when adding 50 g/L zeolite into the liquid phase of the hydrothermal liquefaction process with an initial ammonium of 78 mg/L and the toxic effect of ammonium on microbe was also decreased. The zeolite not only has an instant effect but also has a long term effect on enhancing the ammonium removal and biomass production. With the present of zeolite, the average ammonium removal efficiency was increased from 80% to 95%. The total suspended biomass density was increased from 1000 mg/L to 1600 mg/L. And the stability of the algal-bacterial system was also obviously improved. Adding zeolite had no significant effect on the organics removal and the SCOD removal efficiency always maintained at 70%-80%.The anaerobic digested effluent was pretreated by electrolytic process instead of dilution, centrifugation or autoclaving process, which decreased the operation cost. The nutrients loadings and suspended solids in the anaerobic digested effluent could be reduced by electro-oxidation, electro-coagulation, electro-flocculation and elecro-flotation. The photosynthetic efficiency was also improved by transparency of the wastewater. Then, the residual nutrients in the wastewater were treated by microalgae and the algal biomass was harvested at the end of cultivation. Zeolite reduced the ammonium concentations by physicochemical process. Zaolite can be used as buffering agent to prevent suddenly increased of ammonium concentrations in the medium, which may cause microbial growth inhibition. Zeolite existed in the reactor also acted as a carrier for microorganisms, especially the nitrifier, attached and growth on their sufaced to form the biofilm to enhance the ammonium and other pollutants removal. Particularly, the physicochemical adsorption of zeolite was completed in a relatively short time after fresh zeolite added into the reactor. While, the promoted MPBR performance was observed even after the zeolite long time existing in the reactor. This indicated that the zeolite not only has instant effect but also has long term effect on enhancing the ammonium removal and biomass production.The finding from this study provides a better way to resolve the inhibition of algal cells by high density or recalcitrant wastewater. The pollutants removal efficiency as well as algal biomass production can be improved by using microalgae for wastewater treatment. It also provided the scientific basis for the E2-Energy recycle proceed in health mode and realize the utilization of waste.